The optical measurement apparatus can measure blood circulation, blood flow and changes of the hemoglobin amount inside the living body by irradiating visible to infrared light onto the part of an object to be examined and by measuring a light that reflects inside the living body. When the optical measurement is performed while the object is loaded with stimulation or task, changes in blood circulation, blood flow and changes in the hemoglobin amount are observed, as compared with that without such stimulation or load. Accordingly, by comparing these changes with the known change patterns, distinctive attributes and characteristics of the subject can be identified.
Since this optical measurement apparatus can obtain information of the living body non-invasively and easily without restraining the subject, the clinical applications of the optical measurement apparatus is being put into clinical use.
The clinical applications of the optical measurement apparatus include the identification of an epileptic focus, the identification of the linguistic area in the pre-examination of epileptic surgery and the diagnosis of cerebral disease. In the examination to identify the linguistic area, for example, the area is identified by measuring local cerebral blood amount change signals for the right and left temporal lobes attributable to the language stimulation load and comparing the range of thus obtained local cerebral blood amount change signals. This is a very important examination to reduce the damage of cerebral function accompanying the removal of an epileptic focus, and a technique for accurately identifying the area is demanded.
However, the superimposition of the local cerebral blood amount change signals by the signals inside the living body and various outside noise signals including apparatus noise and . . . signals attributable to body movement makes it difficult to obtain highly precise local cerebral blood amount change signals.
The moving average and the filtering, as described in Patent Document 1, have been used to remove these noises, but they often failed to remove the noise sufficiently. For example, the spike noise components which generate at CH2 of the graph in FIG. 3 are characterized by a broad frequency band. In order to remove such noises by filtering or moving average, the filter should be applicable to a broader band or the moving average should be applicable for a longer period of time. However, they have such disadvantage that necessary local cerebral blood amount change signals are also removed.    Patent document 1: Japanese Patent Application No. 2002-177281